1. Field of the Invention
The present invention relates to a display device drive circuit. The drive circuit in accordance with the present invention is mounted in a display device that uses light-emitting elements. The light-emitting elements used in the display device are, for example, organic electroluminescent (EL) elements or light-emitting diodes.
2. Description of Related Art
In recent years, display devices using light-emitting elements have been put into practical application. Organic EL elements, light-emitting diodes, and so on, are well-known examples of these light-emitting elements.
Organic EL elements can drive display devices at low DC voltages. Additionally, when compared to light-transmitting type elements, such as liquid crystal elements, organic EL elements provide a broader field of view, a brighter display surface, thinner form and lighter body. Because of this, organic EL elements can be used in large-capacity display devices for various applications.
Organic EL display devices are provided with a large number of organic EL elements arranged in a matrix. The anodes of the organic EL elements in the same column are all connected to the same data line. Additionally, the cathodes of the organic EL elements in the same row are all connected to the same scan line. Transistors for supplying the drive current are connected to each data line. The magnitude of the drive current in normal display devices is controlled by the voltage between the gates and sources of these transistors.
The brightness of the light emitted from an organic EL element depends on the drive current. Consequently, the drive currents supplied to the various data lines must be adjusted in order to improve the image quality of the organic EL display devices. For example, drive currents are set to large values for large display units. Moreover, in order to compensate for manufacturing variability such as variability in the resistor in the interconnections in the peripheral circuitry, it may also be necessary to adjust the drive currents for each individual device.
As described above, the magnitude of the drive current is controlled by the voltage across the gate and source of the electric current supply transistor. However, the characteristics of the transistor vary in accordance with the voltage between the gate and the source. As a result, it is not easy to adjust the drive current with precision for each device.